Pre-packaged Coles lettuce products with use by dates up to and including February 11 are affected, but those with a use-by date on or after February 12 are safe.

Whole lettuces are not affected, Coles said.

Managing Director of Tripod Famers Frank Ruffo, said the company was working closely with health authorities in the interests of public safety.

“We are shocked at the test results because we put public safety first and foremost and comply with all Australian health and safety standards,” he said.

“We will be doing everything within our power to determine how this has happened.

“We have commenced a thorough investigation and will work with health authorities to ensure we get to the bottom of this.”

Tripod Farmers has farms in Gippsland, Western Melbourne and Mildura, with a processing facility in Bacchus Marsh.

The Victorian Department of Health and Human Services Senior Medical Advisor Dr Finn Romanes said he expected more cases to emerge.

Recalled bagged spinachSource:Supplied

Varieties of packaged lettuce and spinach have been removedSource:Supplied

“We know that the lettuce products involved, that there are a number of products, and that the distribution of those products is very widespread particularly in Victoria,” he said.

“When we identify an outbreak of salmonella, usually the people, or the cases that we’re aware of are the tip of an iceberg,” he said.

He said people with these products should either return them to the place of purchase or discard them.

“Normally we only see a handful of cases of this strain each year, but so far this year there have been 28 adult cases of Salmonella anatum — mostly adults — notified to the Department,” Dr Romanes said.

“As a result of following up the food histories of a number of people we have discovered a common source — the Tripod Farmers lettuce.

“Tests of three products from two batches have also tested positive.”

But frustrated customers searching for information took to Coles’ and Woolworths’ facebook pages had plenty of questions, but no answers by late yesterday afternoon.

“What is happening about the recall on the pre packed salad, need to know dates etc, have consumed some last week and had upset stomach, need to know if we can at least get a refund,” wrote one concerned Coles customer.

Over on Woolworths’ facebook, one Western Australian customer posted “Thanks for the Salmonella Woolies! Might want to remove washed and ready to eat from your salad bags!” He then posted a copy of his pathology report.

The elderly, those with another medical condition (such as a weakened immune system) or are malnourished are more prone to the illness, with symptoms occurring between 6 to 72 hours after the bacteria is ingested.

The most common symptoms include: diarrhoea, which may contain blood or mucous; fever; headache; stomach cramps; nausea; vomiting, and dehydration, especially among infants and the elderly.